ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 699 



thalliis, there are also small and large hour-glass cells, which grow out to 

 form unicellular haptera. In the formation of zoospores, an entire 

 vesicle is fertilised. The zoospores which escape through numerous 

 holes have a red eye-spot, and in V. macropMjsa four cilia, in V. utrku- 

 larls two. They are asexual, and germinate easily. The mass of 

 zoospores is net-shaped. After fertilisation the vesicle goes to pieces. 



Structure and Classification of the Siphonales.* — C. A. Bessey 

 discusses this subject, and makes an attempt to arrange the ccenocytic 

 algse in accordance with the theory that they have been derived from 

 multicellular filamentous algaj of the Ulotrichoid type, among the 

 Confervales, where the segments of the filament are true cells, each 

 having a single nucleus. Near to these are placed the Cladophoracete, 

 in which the segments of the filaments are more or less elongated 

 coenocytes, each of which contains from one to many nuclei. The 

 author considers that Cladoplioraceaj, united with two or three other 

 families, should form an intermediate group between the strictly cellular 

 and the completely ccenocytic orders : an arrangement which is followed 

 by Blackman and Tansley, and by Oltmanns. Siphonese and Siphono- 

 cladacese are not retained as two sub-orders. The Cladophoracese are 

 regarded as having been derived from the Ulotrichacese, and have 

 . themselves given rise to two distinct phyla : (1) the Vaucheria series ; 

 and (2) the Acetabular ia series. Tlie evolutionary steps marked by 

 different genera are shown in a diagram. The author acknowledges 

 18 pretty well marked families in Siphonales, of which 11 belong to the 

 Algse. A key to these 11 is given, followed by keys to the genera in. 

 each family and a short diagnosis of each genus. 



Observations on Spirogyra.f — F. E. Fritsch and F. Rich publish 

 the first of a series of studies on the occurrence and reproduction of 

 British fresh-water alga3 in nature. In the present paper they deal with 

 Spiroiiyra, of which alga they have examined extensive material at 

 various seasons from ponds situated mainly in the south of England. 

 The authors present their results under the heads : The occurrence of 

 Spirogijra in nature ; the reproduction of Spirogyra in nature : and 

 points of systematic interest. They summarise their results as follows : 

 The species of Spirogyra which we have examined are either purely 

 vernal or exhibit both a vernal and an autumnal phase with an inter- 

 vening period of scarcity or complete disappearance : it seems possible 

 that there is also a period of disappearance in mid-winter, but this is not 

 certainly established. The autumnal re-appearance of certain species of 

 Spirogyra is no doubt due to the influence of certain combinations of 

 external factors causing a small number of zygospores to germinate ; in 

 the absence of these conditions there may be no autumnal phase. 

 Abnormal meteorological conditions may bring about abnormal absence 

 or occurrence of Spirogyra. 



Reproduction takes place ordinarily in the vernal phase, and is most 

 probably the result of certain periodically recurring combinations of 

 factors, which vary for different species. A considerable number of 



* Trans. Amer. Micro. Soc, xxvii. (1907) pp. 47-62 (1 pi.), 

 t Ann. of Bot., xxi. (1907) pp. 423-36. 



